Regex Config Pattern

Regex Configuration Patterns

Generates the correct regex patterns for config_manager.py save operations that update BobConfig.py.

When to Use

• Adding save logic to config_manager.py
• Creating regex patterns for new config parameters
• Troubleshooting regex matching issues
• Understanding the config save pattern

Pattern Structure

All config saves follow this pattern:

content = re.sub(
    r'PATTERN_TO_MATCH',
    f'REPLACEMENT_STRING',
    content
)
changes_made.append(f"PARAM_NAME = {value}")

Type-Specific Patterns

Boolean Parameters

BobConfig.py:

FEATURE_ENABLED: bool = True

Regex Pattern:

if 'feature_enabled' in section:
    content = re.sub(
        r'FEATURE_ENABLED:\s*bool\s*=\s*(True|False)',
        f'FEATURE_ENABLED: bool = {section["feature_enabled"]}',
        content
    )
    changes_made.append(f"FEATURE_ENABLED = {section['feature_enabled']}")

Pattern Breakdown:

• FEATURE_ENABLED: - Exact parameter name + colon
• \s* - Zero or more whitespace
• bool - Type annotation
• \s*=\s* - Equals sign with optional whitespace
• (True|False) - Either True or False (capture group)

Integer Parameters

BobConfig.py:

MAX_RETRIES: int = 3

Regex Pattern:

if 'max_retries' in section:
    content = re.sub(
        r'MAX_RETRIES:\s*int\s*=\s*\d+',
        f'MAX_RETRIES: int = {section["max_retries"]}',
        content
    )
    changes_made.append(f"MAX_RETRIES = {section['max_retries']}")

Pattern Breakdown:

• \d+ - One or more digits (matches any integer)

Float Parameters

BobConfig.py:

THRESHOLD: float = 0.5
PERCENTAGE: float = 10.0

Regex Pattern:

if 'threshold' in section:
    content = re.sub(
        r'THRESHOLD:\s*float\s*=\s*[\d.]+',
        f'THRESHOLD: float = {float(section["threshold"])}',
        content
    )
    changes_made.append(f"THRESHOLD = {section['threshold']}")

Pattern Breakdown:

• [\d.]+ - One or more digits or decimal points
• Note: float() conversion in f-string ensures proper formatting

Important: Always cast to float in f-string!

# ✓ Correct
f'THRESHOLD: float = {float(section["threshold"])}'

# ✗ Wrong - may produce "0.5" vs "0.50"
f'THRESHOLD: float = {section["threshold"]}'

String Parameters

BobConfig.py:

MODEL_NAME: str = "default"
API_URL: str = "http://localhost:5000"

Regex Pattern:

if 'model_name' in section:
    content = re.sub(
        r'MODEL_NAME:\s*str\s*=\s*"[^"]*"',
        f'MODEL_NAME: str = "{section["model_name"]}"',
        content
    )
    changes_made.append(f"MODEL_NAME = {section['model_name']}")

Pattern Breakdown:

• "[^"]*" - Matches string in double quotes
• [^"] - Any character except double quote
• * - Zero or more characters

For single quotes:

r"MODEL_NAME:\s*str\s*=\s*'[^']*'"
f"MODEL_NAME: str = '{section[\"model_name\"]}'"

Optional Parameters

BobConfig.py:

API_KEY: Optional[str] = None

Regex Pattern:

if 'api_key' in section:
    content = re.sub(
        r'API_KEY:\s*Optional\[str\]\s*=\s*(?:"[^"]*"|None)',
        f'API_KEY: Optional[str] = "{section["api_key"]}" if section["api_key"] else "None"',
        content
    )
    changes_made.append(f"API_KEY = {section['api_key']}")

Pattern Breakdown:

• Optional\[str\] - Type annotation (brackets escaped)
• (?:"[^"]*"|None) - Non-capturing group: either string or None
• "[^"]*" - String in quotes
• | - OR
• None - Literal None

List Parameters

BobConfig.py:

ALLOWED_MODELS: List[str] = ["model1", "model2"]

Regex Pattern (Complex):

if 'allowed_models' in section:
    models_str = str(section["allowed_models"])  # Convert list to string
    content = re.sub(
        r'ALLOWED_MODELS:\s*List\[str\]\s*=\s*\[.*?\]',
        f'ALLOWED_MODELS: List[str] = {models_str}',
        content
    )
    changes_made.append(f"ALLOWED_MODELS = {len(section['allowed_models'])} items")

Pattern Breakdown:

• \[.*?\] - Matches list brackets with any content
• .*? - Non-greedy match (minimum characters)

Common Pattern Variations

With Comments

BobConfig.py:

MAX_FPS: int = 30  # Maximum frames per second

Regex (preserves comment):

r'MAX_FPS:\s*int\s*=\s*\d+(\s*#.*)?'

Pattern Breakdown:

• (\s*#.*)? - Optional group for comment
• \s*# - Whitespace + hash
• .* - Rest of comment
• ? - Group is optional

Multiline Parameters

BobConfig.py:

LONG_LIST: List[str] = [
    "item1",
    "item2"
]

Use re.DOTALL flag:

content = re.sub(
    r'LONG_LIST:\s*List\[str\]\s*=\s*\[.*?\]',
    f'LONG_LIST: List[str] = {value}',
    content,
    flags=re.DOTALL
)

Complete Save Method Template

def save_<section>_settings(self, settings: Dict) -> Dict:
    """Save <section> settings to BobConfig.py"""
    try:
        config_path = Path(__file__).parent.parent / 'BobConfig.py'

        if not config_path.exists():
            return {'success': False, 'message': f'Config file not found: {config_path}'}

        # Read current config
        with open(config_path, 'r', encoding='utf-8') as f:
            content = f.read()

        changes_made = []

        # Boolean parameter
        if 'bool_param' in settings['section']:
            content = re.sub(
                r'BOOL_PARAM:\s*bool\s*=\s*(True|False)',
                f'BOOL_PARAM: bool = {settings["section"]["bool_param"]}',
                content
            )
            changes_made.append(f"BOOL_PARAM = {settings['section']['bool_param']}")

        # Integer parameter
        if 'int_param' in settings['section']:
            content = re.sub(
                r'INT_PARAM:\s*int\s*=\s*\d+',
                f'INT_PARAM: int = {settings["section"]["int_param"]}',
                content
            )
            changes_made.append(f"INT_PARAM = {settings['section']['int_param']}")

        # Float parameter
        if 'float_param' in settings['section']:
            content = re.sub(
                r'FLOAT_PARAM:\s*float\s*=\s*[\d.]+',
                f'FLOAT_PARAM: float = {float(settings["section"]["float_param"])}',
                content
            )
            changes_made.append(f"FLOAT_PARAM = {settings['section']['float_param']}")

        # String parameter
        if 'str_param' in settings['section']:
            content = re.sub(
                r'STR_PARAM:\s*str\s*=\s*"[^"]*"',
                f'STR_PARAM: str = "{settings["section"]["str_param"]}"',
                content
            )
            changes_made.append(f"STR_PARAM = {settings['section']['str_param']}")

        if not changes_made:
            return {'success': False, 'message': 'No valid settings to update'}

        # Write updated config
        with open(config_path, 'w', encoding='utf-8') as f:
            f.write(content)

        logger.info(f"Updated settings: {', '.join(changes_made)}")

        return {
            'success': True,
            'message': f'Settings saved. Updated: {", ".join(changes_made)}'
        }

    except Exception as e:
        logger.error(f"Error saving settings: {e}", exc_info=True)
        return {'success': False, 'message': f'Error: {str(e)}'}

Testing Regex Patterns

Python REPL Test:

import re

# Test content
content = "THRESHOLD: float = 0.5  # Detection threshold"

# Test pattern
pattern = r'THRESHOLD:\s*float\s*=\s*[\d.]+'
replacement = f'THRESHOLD: float = {float(10.0)}'

result = re.sub(pattern, replacement, content)
print(result)
# Output: THRESHOLD: float = 10.0  # Detection threshold

Online Regex Tester:

• https://regex101.com/ (Python flavor)
• Paste BobConfig.py line
• Test pattern
• Verify match and replacement

Common Mistakes

1. Wrong Pattern for Float

# ✗ Wrong - only matches integers
r'THRESHOLD:\s*float\s*=\s*\d+'

# ✓ Correct - matches floats with decimals
r'THRESHOLD:\s*float\s*=\s*[\d.]+'

2. Missing Float Conversion

# ✗ Wrong - may lose precision
f'THRESHOLD: float = {value}'

# ✓ Correct - explicit float conversion
f'THRESHOLD: float = {float(value)}'

3. Greedy vs Non-Greedy

# ✗ Wrong - matches too much (greedy)
r'PARAM:\s*str\s*=\s*".*"'  # Matches from first to LAST quote

# ✓ Correct - matches minimal (non-greedy)
r'PARAM:\s*str\s*=\s*"[^"]*"'  # Matches one string

4. Not Escaping Special Characters

# ✗ Wrong - brackets are regex special chars
r'List[str]'

# ✓ Correct - escape brackets
r'List\[str\]'

5. Missing changes_made Entry

# ✗ Wrong - silent success, no tracking
content = re.sub(pattern, replacement, content)

# ✓ Correct - track changes
content = re.sub(pattern, replacement, content)
changes_made.append(f"PARAM = {value}")

Debugging Regex Issues

Pattern doesn't match:

1. Copy actual line from BobConfig.py
2. Test in regex101.com with Python flavor
3. Check for extra whitespace or comments
4. Verify type annotation exact spelling

Match but wrong replacement:

1. Check capture groups in pattern
2. Verify f-string uses correct variable
3. Test with print before writing file

Multiple matches:

1. Make pattern more specific (add context)
2. Use parameter name prefix (e.g., VISION_THRESHOLD)
3. Check for duplicates in BobConfig.py

Quick Reference

Pro Tips

1. Test patterns first - Use regex101.com before coding
2. Copy exact lines - Use actual BobConfig.py content for testing
3. Be specific - Include parameter name to avoid false matches
4. Track changes - Always append to changes_made list
5. Handle errors - Wrap in try/except
6. Log changes - Use logger.info for change tracking
7. Validate input - Check types before regex